exporter-exporter - add support for serving files directly

README.md

@@ -99,6 +99,12 @@ modules:
       env:
         THING: "1"
         THING2: "2"
+
+  somefile:
+    method: file
+    file:
+      path: /tmp/myfile.prometheus.txt
+      use_mtime: true
 ```
 
 In your prometheus configuration

config.go

@@ -45,6 +45,7 @@ type moduleConfig struct {
 
 	Exec execConfig `yaml:"exec"`
 	HTTP httpConfig `yaml:"http"`
+	File fileConfig `yaml:"file"`
 
 	name string
 }
@@ -78,6 +79,13 @@ type execConfig struct {
 	mcfg *moduleConfig
 }
 
+type fileConfig struct {
+	Path      string                 `yaml:"path"`
+	UseMtime  bool                   `yaml:"use_mtime"`
+	IsGlob    bool                   `yaml:"glob"`
+	mcfg *moduleConfig
+}
+
 func readConfig(r io.Reader) (*config, error) {
 	buf := bytes.Buffer{}
 	io.Copy(&buf, r)
@@ -168,6 +176,10 @@ func checkModuleConfig(name string, cfg *moduleConfig) error {
 		if len(cfg.Exec.XXX) != 0 {
 			return fmt.Errorf("unknown exec module configuration fields: %v", cfg.Exec.XXX)
 		}
+	case "file":
+		if cfg.File.Path == "" {
+			return fmt.Errorf("Path argument for file module is mandatory")
+		}
 	default:
 		return fmt.Errorf("unknown module method: %v", cfg.Method)
 	}

file.go

@@ -0,0 +1,190 @@
+// Copyright 2016 Qubit Ltd.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/expfmt"
+	log "github.com/sirupsen/logrus"
+)
+
+var (
+	fileStartsCount = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "expexp_command_starts_total",
+			Help: "Counts of command starts",
+		},
+		[]string{"module"},
+	)
+	fileFailsCount = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "expexp_command_fails_total",
+			Help: "Count of commands with non-zero exits",
+		},
+		[]string{"module"},
+	)
+)
+
+func readFileWithDeadline(path string, t time.Time) ([]byte, time.Time, error) {
+	f, err := os.Open(path)
+	mtime := time.Time{}
+	if err != nil {
+		return nil, mtime, err
+	}
+	defer f.Close()
+	f.SetDeadline(t)
+
+	var size int
+	if info, err := f.Stat(); err == nil {
+		size64 := info.Size()
+		if int64(int(size64)) == size64 {
+			size = int(size64)
+		}
+		if info.Mode().IsRegular() {
+			mtime = info.ModTime()
+		}
+	}
+	size++ // one byte for final read at EOF
+
+	// If a file claims a small size, read at least 512 bytes.
+	// In particular, files in Linux's /proc claim size 0 but
+	// then do not work right if read in small pieces,
+	// so an initial read of 1 byte would not work correctly.
+	if size < 512 {
+		size = 512
+	}
+
+	data := make([]byte, 0, size)
+	for {
+		if time.Now().After(t) {
+			return data, mtime, os.ErrDeadlineExceeded
+		}
+		if len(data) >= cap(data) {
+			d := append(data[:cap(data)], 0)
+			data = d[:len(data)]
+		}
+		n, err := f.Read(data[len(data):cap(data)])
+		data = data[:len(data)+n]
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			return data, mtime, err
+		}
+	}
+}
+
+var (
+	mtimeName = "expexp_file_mtime_timestamp"
+	mtimeHelp = "Time of modification of parsed file"
+	mtimeType = dto.MetricType_GAUGE
+	mtimeLabelModule = "module"
+	mtimeLabelPath   = "path"
+)
+
+func (c fileConfig) GatherWithContext(ctx context.Context, r *http.Request) prometheus.GathererFunc {
+	return func() ([]*dto.MetricFamily, error) {
+
+		errc := make(chan error, 1)
+		datc := make(chan []byte, 1)
+		timec := make(chan time.Time, 1)
+		go func() {
+			deadline, ok := ctx.Deadline()
+			if ! ok { deadline = time.Now().Add(time.Minute * 5) }
+			dat, mtime, err := readFileWithDeadline(c.Path, deadline)
+			errc <- err
+			if err == nil {
+			    datc <- dat
+			    timec <- mtime
+			}
+			close(errc)
+			close(datc)
+			close(timec)
+		}()
+
+		err := <- errc
+		if err != nil {
+			log.Warnf("File module %v failed to read file %v, %+v", c.mcfg.name, c.Path, err)
+			fileFailsCount.WithLabelValues(c.mcfg.name).Inc()
+			if err == context.DeadlineExceeded || err == os.ErrDeadlineExceeded {
+				proxyTimeoutCount.WithLabelValues(c.mcfg.name).Inc()
+			}
+			return nil, err
+		}
+		dat := <- datc
+		mtime := <- timec
+		var prsr expfmt.TextParser
+
+		var mtimeBuf *int64 = nil
+		if ! mtime.IsZero() {
+			mtimeBuf = new(int64)
+			*mtimeBuf = mtime.UnixMilli()
+		}
+
+		var result []*dto.MetricFamily
+		mfs, err := prsr.TextToMetricFamilies(bytes.NewReader(dat))
+		if err != nil {
+			proxyMalformedCount.WithLabelValues(c.mcfg.name).Inc()
+			return nil, err
+		}
+		for _, mf := range mfs {
+			if c.UseMtime && mtimeBuf != nil {
+				for _, m := range mf.GetMetric() {
+					m.TimestampMs = mtimeBuf
+				}
+			}
+			result = append(result, mf)
+		}
+		if !mtime.IsZero() {
+			v := float64(mtime.Unix())
+			g := dto.Gauge { Value: &v, }
+			l := make([]*dto.LabelPair, 2)
+			l[0] = &dto.LabelPair{
+				Name:&mtimeLabelModule,
+				Value:&c.mcfg.name,
+			}
+			l[1] = &dto.LabelPair{
+				Name:&mtimeLabelPath,
+				Value:&c.Path,
+			}
+			m := dto.Metric {
+				Label: l,
+				Gauge: &g,
+			}
+			mf := dto.MetricFamily{
+				Name: &mtimeName,
+				Help: &mtimeHelp,
+				Type: &mtimeType,
+			}
+			mf.Metric = append(mf.Metric, &m)
+			result = append(result, &mf)
+		}
+		return result, nil
+	}
+}
+
+func (c fileConfig) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	ctx := r.Context()
+	g := c.GatherWithContext(ctx, r)
+	promhttp.HandlerFor(g, promhttp.HandlerOpts{}).ServeHTTP(w, r)
+}

main.go

@@ -502,6 +502,9 @@ func (m moduleConfig) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	case "http":
 		m.HTTP.mcfg = &m
 		m.HTTP.ServeHTTP(w, nr)
+	case "file":
+		m.File.mcfg = &m
+		m.File.ServeHTTP(w, nr)
 	default:
 		log.Errorf("unknown module method  %v\n", m.Method)
 		proxyErrorCount.WithLabelValues(m.name).Inc()